Maximum Removal Capacity Research Articles

Crayfish shell waste as safe biosorbent for removal of Cu2+ and Pb2+ from synthetic wastewater

Crayfish shell is an abundant natural waste and is also a potential biosorbent for pollutants, especially, heavy metals. In this study, the safety of the use of crayfish shell as a biosorbent was first assessed by release experiments involving primary heavy metal ions, such as Cu2+, Zn2+, and Cr3+, in aqueous solution under different environmental conditions. The release concentrations of heavy metals were dependent on pH, ionic strength, and humic acid; and the maximum release concentrations of heavy metals were still lower than the national standard. Specifically, Cu2+ and Pb2+ removal by crayfish shell in synthetic wastewater was investigated. The removal process involved biosorption, precipitation, and complexation, and the results indicate that crayfish shell is an excellent biosorbent for Cu2+ and Pb2+ removal. The precipitation step is particularly dependent on Ca species, pH, and temperature. The maximum removal capacities of Pb2+ and Cu2+ were 676.20 and 119.98 mg/g, respectively. The related precipitates and the generated complex products include Cu2CO3(OH)2, Ca2CuO3, CuCO3, Pb2CO3(OH)2, CaPb3O4, and PbCO3.

Preparation of diethylenetriamine-functionalized thiosulfate intercalated ZnNiAl-LDHs and its removal behavior and mechanism of U(VI)

A new composite material, diethylenetriamine-functionalized thiosulfate intercalated zinc-nickel-aluminum hydrotalcite (DETA-ZnNiAl-S2O32−-LDHs), was synthesized by introducing S2O32− between ZnNiAl-LDHs layers and grafting diethylenetriamine for functionalization modification. The morphological structure and physicochemical properties of samples were analyzed using XRD, FTIR, SEM and BET characterization. By analyzing the results of the batch removal experiments, it was found that the removal process of U(VI) by DETA-ZnNiAl-S2O32−-LDHs was more consistent with the pseudo-second-order and Langmuir isotherm models, and the process was endothermic and spontaneous. The maximum removal capacity of DETA-ZnNiAl-S2O32−-LDHs reached 558.66 mg/g at pH of 6, contact time of 6 h, sample dosage of 0.004 g and temperature of 313 K. The removal of U(VI) by DETA-ZnNiAl-S2O32−-LDHs involved adsorption and reduction: U(VI) bound to the laminar hydroxyl group and diethylenetriamine of the material through surface complexation, while the thiosulfate in the material reduced U(VI) to U(IV) and then removed it. In addition, DETA-ZnNiAl-S2O32−-LDHs still showed superior removal performance under high salinity and complex co-existing ion environment. The results suggest that DETA-ZnNiAl-S2O32−-LDHs have potential applications in the efficient remediation of radioactive wastewater.

Metal(loid)s removal by zeolite-supported iron particles from mine contaminated groundwater: Performance and mechanistic insights

Iron-based materials have been widely investigated because of their high surface reactivity, which has shown potential for the remediation of metal(loid)s in groundwater. However, the disadvantages of structural stability and economic feasibility always limit their application in permeable reactive barrier (PRB) technology. In this study, zeolite-supported iron particles (Zeo-Fe) were synthesized by an innovative low-cost physical preparation method that is suitable for mass production. The removal efficiency and mechanism of typical metal(loid)s (Pb2+, Cd2+, Cr6+ and As3+) were subsequently investigated using various kinetic and equilibrium models and characterization methods. The results of scanning electron microscopy and energy dispersive spectrometry (SEM-EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) confirmed that zero valent iron (Fe0) and oxidation product (Fe3O4) were successfully loaded and efficiently dispersed on zeolite. The synthesized Zeo-Fe exhibited excellent adsorption and redox capacities for the cations Pb2+, Cd2+ and anions Cr6+, As3+. The increase in the pH resulting from Fe0 corrosion also enhanced the precipitation of Fe-metal(loid)s. The maximum removal capacity for Pb2+, Cd2+, Cr6+ and As3+ was up to 70.00, 9.12, 2.35 and 0.36 mg/g, respectively. The removal processes were well described by the pseudo-second-order kinetic model for Pb2+ and Cd2+, Lagergren pseudo first-order kinetics model for As3+ and double phase first order kinetics model l for Cr6+. Cr6+ was rapidly reduced to Cr3+ by the Fe0 stabilized on Zeo-Fe, and the oxidation of As3+ to As5+ was attributed to the Fe0/Fe2+ oxidation process at the interface over time, which was further demonstrated by the mineral phase and element valence analyses of reacted Zeo-Fe. The removal mechanism for metal(loid)s was a combination of physical and chemical processes, including adsorption, co-precipitation and reduction-oxidation. Conclusively, Zeo-Fe has been shown to have potential as an effective and economical material for removing various metal(loid)s used in PRB.

Ultrasonic-assisted preparation of interlaced layered hydrotalcite (U–Fe/Al-LDH) for high-efficiency removal of Cr(VI): Enhancing adsorption-coupled reduction capacity and stability

Cr(VI) contamination in aquatic systems has been a challenge for environmental science researchers. To environmental-friendly, stable, and efficiently remove Cr (VI), a novel layered double hydroxide was prepared through the ultrasonic-assisted co-precipitation method. The ultrasonic-assisted step prevented the Fe2+ oxidation, improved the morphology and performance, and finally, the adsorption-coupled reduction capacity and stability were enhanced. By adding U–Fe/Al-LDH (1.0 g/L) for Cr(VI) (100 mg/L), the removal rate reached 82.24%. The removal data were well fitted by the pseudo-second-order kinetic and Langmuir isotherm model. Using U–Fe/Al-LDH can be performed over a wide pH range (2–10), with a theoretical maximum removal capacity of 118.65 mg/g. The Cr(VI) with high toxicity was adsorbed and reduced to low-toxicity Cr(III). In the final phase, stable Cr(III) complex precipitates were generated. After 30 days, the dynamic leaching amounts of total Cr in used U–Fe/Al-LDH-2 were 0.1052 mg/L. Combined with the results of the influence experiment of coexisting anions and oxidants and the SO42− release experiment, the stability of the removal effect and the safety of U–Fe/Al-LDH were proved. In conclusion, U–Fe/Al-LDH-2 is a promising remediation agent and a feasible Cr(VI) removal method for the practical remediation.

Ion Exchange Biomaterials to Capture Daptomycin and Prevent Resistance Evolution in Off-Target Bacterial Populations.

Daptomycin (DAP), a cyclic anionic lipopeptide antibiotic, is among the last resorts to treat multidrug-resistant Gram-positive bacterial infections, caused by vancomycin-resistant Enterococcus faecium or methicillin-resistant Staphylococcus aureus. DAP is administered intravenously, and via biliary excretion, ∼5-10% of the intravenous DAP dose arrives in the gastrointestinal (GI) tract where it drives resistance evolution in the off-target populations of E. faecium bacteria. Previously, we have shown in vivo that the oral administration of cholestyramine, an ion exchange biomaterial (IXB) sorbent, prevents DAP treatment from enriching DAP resistance in the populations of E. faecium shed from mice. Here, we investigate the biomaterial-DAP interfacial interactions to uncover the antibiotic removal mechanisms. The IXB-mediated DAP capture from aqueous media was measured in controlled pH/electrolyte solutions and in the simulated intestinal fluid (SIF) to uncover the molecular and colloidal mechanisms of DAP removal from the GI tract. Our findings show that the IXB electrostatically adsorbs the anionic antibiotic via a time-dependent diffusion-controlled process. Unsteady-state diffusion-adsorption mass balance describes the dynamics of adsorption well, and the maximum removal capacity is beyond the electric charge stoichiometric ratio because of DAP self-assembly. This study may open new opportunities for optimizing cholestyramine adjuvant therapy to prevent DAP resistance, as well as designing novel biomaterials to remove off-target antibiotics from the GI tract.

Ternary metal oxide nanocomposite for room temperature H2S and SO2 gas removal in wet conditions

A ternary Mn–Zn–Fe oxide nanocomposite was fabricated by a one-step coprecipitation method for the remotion of H2S and SO2 gases at room temperature. The nanocomposite has ZnO, MnO2, and ferrites with a surface area of 21.03 m2 g−1. The adsorbent was effective in mineralizing acidic sulfurous gases better in wet conditions. The material exhibited a maximum H2S and SO2 removal capacity of 1.31 and 0.49 mmol g−1, respectively, in the optimized experimental conditions. The spectroscopic analyses confirmed the formation of sulfide, sulfur, and sulfite as the mineralized products of H2S. Additionally, the nanocomposite could convert SO2 to sulfate as the sole oxidation by-product. The oxidation of these toxic gases was driven by the dissolution and dissociation of gas molecules in surface adsorbed water, followed by the redox behaviour of transition metal ions in the presence of molecular oxygen and water. Thus, the study presented a potential nanocomposite adsorbent for deep desulfurization applications.

A novel oxalated zero-valent iron nanoparticle for Pb(II) removal from aqueous solution: Performance and synergistic mechanisms

A novel oxalated zero-valent iron nanoparticle (Ox-nZVI) was synthesized using one-step and two-step modification to investigate the performance and synergistic mechanisms for aqueous Pb(II) removal. Batch experiments showed the maximum removal capacity of Ox-nZVI toward Pb(II) reached 527 mg/g along with 7.87 mg/g Fe release (R2 = 0.989) at a pH of 7.0, contact time of 1440 min, initial Pb(II) concentration of 250 mg/L and temperature at 25 °C. The characterization results suggested reduction, adsorption and co-precipitation were synergistically realized between Pb(II) and Ox-nZVI. Oxalate modification favored steric stability by coverage of membrane-like flakes on the outer surface of nanospheres, leading to more Pb(II) reduced to Pb0 by capturing electrons from the oxidation of Fe0 into iron oxides including Fe3O4, Fe2O3 and FeOOH. The Pb(II) complexes existed on the active sites of Ox-nZVI surface via FeC2O4-, FeOOH and FeOH groups. The adsorption process was best fitted with pseudo-second-order kinetic model and Langmuir isotherm through surface mass transfer and interparticle diffusion. The existence of PbO, Pb3(CO3)2(OH)2 and PbFe12O19 was attributed to the co-precipitation of Pb(II) with hydroxyl ion and atmospheric CO2. This study provided a promising iron-based nanomaterial with surface modification strategy for effective and long-term treatment of Pb(II) from aqueous environment.

Insights into olation reaction-driven coagulation and adsorption: A pathway for exploiting the surface properties of biochar

In this study, characterization of biochar for the efficient removal of cadmium was investigated. Biochar has a specific distribution of functional groups on its surface and has a natural electronegativity. Using carbonate as an olation reagent, the biochar coagulates with the olation reaction products. The maximum removal capacity reached 430.4 mg/g at pH = 4 (Langmuir Fit). Carbonate hydrolyzed on the surface of biochar, Cd2+ in solution undergoes olation with OH− and forms specially structured nanochains that are positively charged on the surface. The biochar with electronegativity on the surface coagulates with the cadmium hydroxide nanochains, and the cadmium-containing colloid formed by electrostatic attraction settles rapidly and removed. The biochar's re-flocculation performance was consistent, and the loadings could be changed to effectively remove cadmium while keeping the pH neutral at equilibrium.

Removal of anionic and cationic dyes from aqueous solution using thermo- and pH-responsive amphiphilic copolymers

Amphiphilic copolymers exhibiting thermally induced phase segregation in water hold great potential as smart flocculants for water purification. Herein, we report the preparation of thermo- and pH-responsive copolymers based on oligo(ethylene glycol) methacrylate (OEGMA), dimethylaminoethyl acrylate (DMAEA) and pentafluorostyrene (PFS), and their use as thermally induced adsorbents for the removal of anionic and cationic dyes from water. The copolymer self-assembly behaviour in water was first studied as a function of concentration and pH. Then, the potential to remove thiazole yellow G (TYG) and rhodamine B (RhB) was investigated as a function of pH and dye concentration, highlighting that dye removal is mediated by hydrophobic and electrostatic interactions. As regards TYG, at pH 4 a removal capacity (RC) of about 80 mg/g, corresponding to a 97 % dye removal efficiency, was achieved at 800 mg/L TYG. In the case of RhB, a maximum RC value of 32 mg/g was obtained at pH 10. The results reported herein show that these copolymers represent a versatile platform to remove water-soluble organic dyes depending on pollutant concentration and pH conditions.

Efficient adsorption and reduction of Cr(VI) from aqueous solution by Santa Barbara Amorphous-15 (SBA-15) supported Fe/Ni bimetallic nanoparticles

Nanoscale zero-valent iron (nZVI or Fe0) can rapidly reduce Cr(VI) contaminants in the water environment, but the agglomeration and passivation of the Fe0 system have adverse effects on its application. In this study, a novel mesoporous Santa Barbara Amorphous-15 supported Fe/Ni bimetallic composite (SBA-15@Fe/Ni) is proposed to remove Cr(VI). The proposed material can enhance the stability and removal capacity of the nZVI system. The results show that the unique six-way through-hole structure of SBA-15 provides a place for the dispersion of Fe0 particles. Meanwhile, SBA-15 effectively alleviates the accumulation of Fe0 particles. The removal efficiency of SBA-15@Fe/Ni is better than two single systems (SBA-15 and Fe/Ni). The removal efficiency of SBA-15@Fe/Ni towards Cr(VI) can reach 97.62% after 60 min at pH 4.0. SBA-15@Fe/Ni still maintains excellent performance in the presence of various competitive ions (Cl-, SO42-, CO32–, NO3–). At 298 K, the maximum removal capacity of SBA-15@Fe/Ni towards Cr(VI) is 180.99 mg/g. The possible removal process of SBA-15@Fe/Ni towards Cr(VI) is divided into the following steps: First, Cr(VI) is attracted into the vicinity of the SBA-15@Fe/Ni channel by the electrostatic attraction; Second, the reduction of Cr(VI) occurs after contacting with the Fe/Ni system, and its driving force mainly comes from nZVI and Fe(II); Furthermore, the introduction of Ni can promote Cr(VI) reduction through electron transfer and catalytic hydrogenation. In conclusion, adopting SBA-15@Fe/Ni to treat chromium contamination is an effective and promising approach.

Chitosan-based electrospun nanofibers mat for the removal of acidic drugs from influent and effluent

In this study, electrospinning was used to synthesize the nanofibers from a blend of chitosan and polyvinyl alcohol (PVA) to remove acidic drugs from wastewater. Fibers with uniform morphology were obtained at voltage of 20 kV, flow rate of 0.2 mL/h, and collection distance of 10 cm. The chemical and physical properties of the produced nanofibers were investigated utilizing a variety of equipment, including SEM, FTIR, XRD, and TGA-DSC. The nanofibers contain active hydroxyl and amino functional groups with an average diameter of 380 nm, according to the characterization results of FTIR and SEM. From the XRD and TGA-DSC analysis, the nanofibers were found to be amorphous and thermally stable at 200 °C. A thermal treatment to the nanofibers was done to reduce the water solubility of the fibers prior to their application for the adsorption of acidic drugs from water systems. Using the ultra-pure water, maximum removal capacities (qm) were calculated from Langmuir isotherm and were found to be 27.85, 1666.66, 166.6, and 1250 mg/g for acetyl salicylic acid, naproxen, fenoprofen, and diclofenac, respectively.

Enhanced Performance of nZVI/MXene@CNTs for Rapid As(III) Removal from Aqueous Solutions

Transition metal compounds demonstrated good performance in the removal of environmentally harmful contaminants, such as arsenic, while the aggregation propensity and poor chemical stability should be noticed. In this study, the nZVI/MXene@CNTs was adequately prepared by liquid reduction precipitation method for adsorption and oxidation of As(III) from the aqueous solution. The results of batch removal experiments showed that the maximum removal capacity of the nZVI/MXene@CNTs for As(III) was 443.32 mg/g with the pH = 3.0 at 25 °C. The effects of initial pH, dosage of materials and ionic strength on As(III) removal were explored. According to the various characterization analyses, the most plausible mechanisms of As(III) removal were the surface complexation, solid phase precipitation and the catalytic oxidation by the •OH. Furthermore, the nZVI/MXene@CNTs could be readily activated and reused via leaching with 0.1 M NaOH solution, due to the three-dimensional mesh intercalation structure. Therefore, it is a potential nanocomplex for removing and recovering As(III) from water with excellent capacity and environmental friendliness.

Biochar from Cyperus alternifolius Linn.: from a waste of phytoremediation processing to efficient depolluting agent.

Phytoremediation is one of the most powerful and viable solutions for developing countries to clean the soil and water bodies from metallic pollutants. Cyperus alternifolius Linn. (CAL), a tropical wetland plant, has been widely researched for removing harmful contaminants due to its hyperaccumulation ability. However, the waste biomass of phytoremediation processing may risk secondary environmental pollution. Thus, the preparation and application of biochar from metal-contaminated plants can be considered a new approach. In a 60-day experiment, CAL plants were irrigated with different concentrations of Zn(II) (200, 700, 1200, 1700, and 2200mg·L-1), and then the plants were converted into biochar via the pyrolysis process. The characteristics of biochar including of surface composition and morphology, phase formation, and optical property were analyzed. The biochar enriched with Zn(II) at 1200mg·L-1 had a bandgap value of 3.17eV and consisted of carbon microparticles intermingled with ZnO and SiO2 nanoparticles. Furthermore, the adsorption and photocatalysis of the biochar were studied in the discolouration of methylene blue (MB), as a test reaction, with the maximum MB removal capacities of 55.2mg·g-1. Such results will serve as the basis for new research aiming at the potential for reusing metal-contaminated plants to produce efficient depolluting biochar.

Iron-biochar production from oily sludge pyrolysis and its application for organic dyes removal.

In this study, a single-step pyrolysis approach was developed to directly convert oily sludge (OS) with high iron content into a magnetic iron-char catalyst for organic dyes removal. Magnetic iron-char catalysts were employed to degrade crystal violet (CV), methylene blue (MB), and sunset yellow (SY). The OC800 iron-char catalyst prepared from OS was not only rich in iron (mainly stable Fe3O4), but also showed favorable pore structures. Effects of operation parameters like temperature, H2O2 dosage, and pH on dye removal based on Fenton degradation were examined. In OC800 Fenton system (0.5mL H2O2, 500mg/L dye concentration, and pH=2 in 50mL solution), the maximum dye removal capacities of SY, CV, and MB were 83.61, 639.19, and 414.25mg/g, respectively. In dyes degradation experiments, the prepared catalyst could be reused (more than 3 successive cycles) due to higher stability and less leaching of iron. One-step pyrolysis of OS with high iron content thereby represents a promising approach to transform sludge waste to functional biochar that removes hazardous dyes.

Fate and mechanistic insights into nanoscale zerovalent iron (nZVI) activation of sludge derived biochar reacted with Cr(VI)

While nanoscale zero-valent iron modified biochar (nZVI-BC) have been widely investigated for the removal of heavy metals, the corrosion products of nZVI and their interaction with heavy metals have not been revealed yet. In this paper, nZVI-BC was synthesized and applied for the removal of Cr(VI). Batch experiments indicated that the adsorption of Cr(VI) fit Langmuir isotherm, with the maximum removal capacity at 172.4 mg/g at pH 2.0. SEM-EDS, BET, XRD, FT-IR, Raman and XPS investigation suggested that reduction of Cr(VI) to Cr(III) was the major removal mechanism. pH played an important role on the corrosion of nZVI-BC, at pH 4.5 and 2.0, FeOOH and Fe3O4 were detected as the major iron oxide, respectively. Therefore, FeOOH-BC and Fe3O4-BC were further prepared and their interaction with Cr were studied. Combining with DFT calculations, it revealed that Fe3O4 has higher adsorption capacity and was responsible for the effective removal of Cr(VI) through electrostatic attraction and reduction under acidic conditions. However, Fe3O4 will continue to convert to the more stable FeOOH, which is the key to for the subsequent stabilization of the reduced Cr(III). The results showed that the oxide corrosion products of nZVI-BC were subjected to the environment, which will eventually affect the fate and transport of the adsorbed heavy metal.

Cellulose-based bio-adsorbent from TEMPO-oxidized natural loofah for effective removal of Pb(II) and methylene blue

Excessive discharge of inorganic and organic contaminants in water poses a serious threat to the ecosystems. However, most synthetic adsorbents lack cost-effectiveness in terms of preparation. Interestingly, loofah sponge (LS) was a natural absorbent that could effectively remove pollutions in wastewater, but its adsorption capacity is barely satisfactory. Herein, we present a novel strategy of TEMPO-oxidized loofah sponge (TOLS) to boost the adsorption performance of LS. The batch experiments demonstrated that the maximum removal capacity of TOLS for Pb(II) and methylene blue (MB) was 96.6 mg/g and 10.0 mg/g, respectively, which were 3.5 and 1.3 times that of pristine LS. Notably, the continuous-flow reaction testing of the mixed solution revealed that the elimination rate of Pb(II) and MB was still better than 90 % even after 16 h. Such excellent performance was benefit from the enhanced specific surface area and surface carboxyl content of TOLS. This work offers new insights into the rational development of multifunctional and inexpensive cellulose-based bio-adsorbents for wastewater remediation.

Confinement of nitrogen-doped porous carbon between graphene layers as a bifunctional electrode for zinc-air battery-driven capacitive deionization

Capacitive deionization (CDI) has attracted considerable attention because of its advantages, which include environmental compatibility, high efficiency and cost effectiveness, while zinc-air batteries (ZABs) are considered to be highly promising next-generation energy conversion devices. The synergy and unity of these two technologies will enable more effective green environmental protection. The desalination effect of CDI devices and the performance of ZABs are closely related to their electrode materials. Here, we used ZIF-8 and graphene oxide as precursors to prepare N-doped porous carbon after high temperature reduction and strong alkali activation. The overall three-dimensional porous carbon-based nanostructure (NJUST) exhibits its potential as a CDI electrode and ZAB cathode to enhance the efficient transport of ions and electrons. The material had a high specific surface area (1426.32 m2/g) and high specific capacitance (127.93F/g). The N-doped porous carbon between porous reduced graphene oxide layers could not only perform the oxygen reduction reaction, but can also provide storage sites for attracting and storing Na ions due to the N atoms it contains. These structural advantages greatly improved the CDI and ZAB performance. The maximum removal capacity in the CDI process was 15.59 mg/g for a 250 mg/L NaCl solution at 1.4 V. Such a configured CDI device was also powered by a Zn-air battery made from the NJUST with an open-circuit voltage of ∼ 1.4 V and had good oxygen reduction reaction activity.

Enhanced capacitive deionization of toxic metal ions using nanoporous walnut shell-derived carbon

Capacitive deionization (CDI) technology differs from traditional demineralization technology. Its desalination effect is mainly dependent on the electrode material and the porous nanostructure which can enhance capacitive deionization performance. Here, a low-cost and eco-friendly CDI technology has been developed to remove divalent ions from water. Using different activators such as KOH, ZnCl2 and K2C2O4 to reconstruct the biomass carbon skeleton, porous carbon material derived from walnut shells was used as symmetric electrodes. The maximum removal capacities in the CDI electrosorption were 17.1 mg/g for Mg2+, 11.99 mg/g for Ca2+, 18.56 mg/g for Pb2+ and 15.52 mg/g for Cd2+. The best effect on formation of micropores and construction of adsorption channels was observed using KOH as activator. The KOH-C had a specific surface area of 1600.34 m2/g and a cumulative pore volume of 0.3561 cm3/g, which provides favorable conditions for ion storage. These results demonstrate that KOH-activated carbon biomass can improve electrosorption performance and has potential as an advanced, inexpensive electrode material for capacitive deionization.

The behavior and mechanism of toxic Pb(II) removal by nanoscale zero-valent iron-carbon materials based on the oil refining byproducts

• nZVI-SBE@C was prepared by anoxic pyrolysis and liquid phase reduction. • When C/Fe = 1/2, nZVI-SBE@C has the best removal efficiency for Pb(II). • Nitrogen atmosphere is more favorable to Pb(II) removal than air atmosphere. • Mechanism: adsorption, electrostatic attraction, ion exchange, reduction. In this study, nanoscale zero-valent iron-carbon materials based on the oil refining byproducts (nZVI-SBE@C) were prepared through anoxic pyrolysis and liquid phase reduction method, and its ability to remove Pb(II) from aqueous solution was tested for the first time. In preparation process, when the mass ratio of C/Fe is 1:2, nZVI-SBE@C has the maximum removal capacity of Pb(II) (182.29 mg/g), which is four times that of SBE@C (51.37 mg/g). In the research of Pb(II) removal behavior, adsorption process by nZVI-SBE@C was fitted well with Langmuir isotherm model and pseudo-second-order kinetic model, and the Langmuir monolayer maximum adsorption capacity of nZVI-SBE@C for Pb(II) was 223.52 mg/g. In the N 2 and air initial atmosphere, Pb(II) removal reached 95.37% and 42.37%, respectively, which were higher than that in blank control group (24.44%). The promotion order of the coexisting cations for nZVI-SBE@C to remove Pb(II) is: Na + > K + > Mg 2+ (the effect of NO 3 – ), and the inhibition order is: Cu 2+ < Fe 3+ < Al 3+ (the effect of the solubility products of precipitation as well as ionic radius). Pb(II) removal by nZVI-SBE@C increased with the increase of initial solution pH (2.30–5.80). Though the characterization of the materials before and after the reaction, meanwhile combining with experimental data, Pb(II) removal mechanisms of nZVI-SBE@C may include surface adsorption, electrostatic attraction, ion exchange, surface complexation and nZVI reduction (small portion).

Arsenate removal from aqueous solutions by Mg/Fe-LDH-modified biochar derived from apple tree residues

ABSTRACT The development of non-toxic and inexpensive materials for arsenic removal is required due to water sources being polluted by arsenic in many countries around the world. The main aim of this study was to characterise the capacity and behaviour of Mg/Fe layered double hydroxides/biochar [Magnesium/Iron-Layered Double Hydroxide (Mg/Fe-LDH)] composite for arsenate adsorption from solution. Apple tree pruning residues were used to produce biochar at 500 °C under oxygen-limited atmosphere. Mg/Fe-LDH-biochar was synthesised using a spontaneous in situ co-precipitation method. Batch experiments were used for the assessment of the kinetics, isotherms, and the effects of initial solution pH (4, 6, 8, and 10), ionic strength (0.01, 0.1, and 0.2 mol L−1), and co-occurring anions (carbonate and phosphate) on the arsenate removal. Scanning electron microscope images showed Mg/Fe-LDH were loaded on the biochar porous structure, and X-ray diffraction analysis affirmed the presence of crystalline LDH minerals in Mg/Fe-LDH-biochar. Surface modification of biochar by Mg/Fe-LDH increased the maximum arsenate adsorption capacity (3.6 mg g−1) ten times compared to unmodified biochar (0.35 mg g−1). Arsenate removal capacity increased from 4.2 % to 54.2 % with modification of biochar by Mg/Fe-based LDH. Kinetic studies indicated that &gt;90 % of Mg/Fe-LDH-biochar arsenate adsorption from a starting concentration of 10 mg L−1 occurred in the first 120 min. Pseudo-second order and Langmuir models described well the kinetics and isotherm of arsenate adsorption by biochar and Mg/Fe-LDH-biochar. Mg/Fe-LDH-biochar showed maximum arsenate removal capacity at pH 6. Increasing solution ionic strength and the presence of phosphate and carbonate anions suppressed arsenate removal by Mg/Fe-LDH-biochar. In summary, surface modification of biochar using Mg/Fe-LDH produced a potentially more cost-effective, locally available, reusable, and non-toxic arsenic adsorbent for decontamination of surface- and groundwater.